1. Field of the Invention
The present invention relates to an optical element positioning apparatus.
2. Description of the Related Art
A semiconductor exposure apparatus used for the lithography process in manufacturing semiconductor devices or micro devices is an apparatus for transferring an original (a reticle) having a number of different kinds of patterns onto a substrate (a silicon wafer). The integration of the semiconductors is increasing year by year, and reducing the aberration and the distortion of a projection optical system is essential in order to make a circuit pattern with high integration.
In order to reduce the aberration or the distortion of the projection optical system, a part of optical elements of the projection optical system is moved in a plurality of axes directions. Japanese Patent Laid-Open No. 2001-343575 discloses a mechanism for moving in an optical axis direction or a three-axis drive mechanism which can perform a tilt drive as a drive in the plurality of axes directions.
Japanese Patent Laid-Open No. 2005-276933 discloses a displacement reduced type parallel link mechanism which can drive an optical element in six degrees of freedom.
However, since the conventional arts described above include problems as follows, the countermeasure has been desired to be taken.
The driving method disclosed in Japanese Patent Laid-Open No. 2001-343575 is one example where sensors and drive mechanisms are arranged around an optical axis at a distance from the optical axis and at an angular interval equal to one another. When such the driving method is applied to the configuration where a movable optical element is arranged outside the optical axis in an optical system including a reflective optical element, there is a problem that a stroke required for the drive mechanism is large in order to rotate around the point on the optical axis. Even if the drive mechanism in which a driving stroke is large is applied, the driving stroke and the rigidity of the mechanism have a tradeoff relation. Therefore, it is difficult to balance both of them, and there is a problem that a desired disturbance vibration property can not be obtained.
In a method of driving optical element disclosed in Japanese Patent Laid-Open No. 2005-276933, the rotation (pitching and rolling) is performed around the axis passing through the center of gravity of an inner ring (a mirror M1). However, a measurement means includes two axes laser interferometers in a plane direction perpendicular to an optical axis and six capacitance sensors which measure the input amount by an actuator. This apparatus does not directly measure in all axes directions of a moving unit. Therefore, the configuration is not enough to position around the axis passing through the center of gravity with high accuracy. In the case where a reflective projection optical system such as an exposure apparatus using EUV light that is a main field of application of the present invention, an angular positioning error of the optical element (in a direction perpendicular to the optical axis) is sensitive since it is a shift of a light beam. Therefore, a measurement method of an optical element with high accuracy has been desired.